The present application is directed in general to systems and methods for communicating in telephone systems and in particular to systems and methods for using portable, wireless telephones integrated with a land-based wired telephone system.
The telephone industry has experienced tremendous growth in the last few years, driven in part by the availability of relatively inexpensive cellular telephone service. In such service, telephone subscribers use portable, battery-powered, hand-held telephone instruments to communicate via RF links with a network of base stations which interface the signals on the RF links into the land-based public telephone network. In such systems, a cellular configuration is generally used in which a particular base station uses certain frequencies to communicate with portable telephones within its "cell" and adjacent base stations use other frequencies to communicate with telephones within their cells. If base stations are sufficiently distant from each other, the same frequencies may be used in both cells so long as neither the base station nor the telephones in one cell generate signals of sufficient power to carry into the other cell. In this way, a limited number of frequencies can be reused in a non-conflicting pattern which provides telephone service throughout a particular geographic area. Of course, as a telephone leaves from one cell to another, the telephone may have to switch frequencies (or "hop" to a new channel) during the middle of an on-going call to avoid broadcasting into a nonadjacent cell which is using the same frequency for a different call.
The use of cellular telephone technology has permitted broad geographic regions to be provided with the availability of many portable telephones. As the popularity of portable telephones has expanded, however, the frequencies (or "channels") have become filled. Within the limited RF bandwidth available for all the competing uses thereof, the solution to cellular overcrowding does not necessarily lie in merely adding additional frequencies or channels within each cell.
It has been proposed in the prior art to utilize smaller cells and to reduce the power of the cellular equipment so that frequencies may be reused in greater proximity to one another. Such a solution is not entirely satisfactory, however, as with much reduced power levels, the signal to noise ratios of the communications may approach levels unacceptable in telephone communications. Along these lines, the prior art has proposed making an office building, a portion of an office building or an office complex a cell site or a small cellular system. Given the crowding on the existing cellular systems, however, such proposed systems are generally limited in the number of portable telephones which they can accommodate.
In many office situations, the persons working in the offices frequently are away from their assigned duty locations for extended periods of time and may even roam throughout the office as their business needs arise. Providing telephone service to such roaming persons in the prior art often meant using call-forwarding schemes or the like to automatically route the call from one location to another. Such systems usually required substantial user input to implement, a drawback in a typical office environment Thus, it is desirable to utilize portable or cellular technology for persons within an office. In a typical office building, the addition of cellular telephones to the already-present land-based system, such as a Private Business Exchange (or "PBX") provides some mobile communication but is insufficient for effective communication. Generally, the portable telephones are tied to a base unit which integrates the RF communications of the cellular system with the public land-based telephone system and not directly with the business person's own PBX. Effectively, such a solution in an office environment yields two independent telephone systems not well tied into each other or coordinated in any way. Additionally, the external structure of the building housing the office may make impractical the transmission of typical cellular RF signals to and from conventional base stations.
A solution to the desire to permit workers to roam within a particular geographic space, such as an office building or a portion of an office building, yet permit such workers to continue to be reachable by the telephone system and to permit the workers to utilize the advantages of the telephone system is to integrate a wireless system with a PBX. With such an integration, incoming calls to workers can be directed by the wireless system to the worker wherever that person may be within the operating range of the system. At the same time, the roaming worker will be able to readily place telephone calls both within and without the office as readily as if sitting at his own desk on the hard-wired system. The roaming worker would also have the benefit of all of the features of the PBX (such as a personalized repertory dialer, special access to restricted circuits, etc.) no matter where the worker may be located within the office.
Desirably, a wireless-PBX system would include a portable telephone unit which is easy to use, lightweight and has an extended battery life. The latter two desires are somewhat at odds with each other inasmuch as battery life often has a direct relation to the size (and weight) of a battery. Accordingly, it is often important in the design of portable units that they be as power-efficient as possible.
Within prior art cellular systems it is known for a particular base station to have associated therewith one or more control channels and several or numerous voice channels. The control channels are used to communicate with the control portions of the portable units to coordinate the use of voice frequencies and to perform an analog of typical central office functions (e.g., dialing a number, ringing the portable unit, etc.). When all of the voice channels within a base station are being utilized, there may no longer be a need for a control channel as there are no more control tasks to be performed until one of the voice channels again becomes available. In such systems, it is desirable to not waste the non-functioning voice channel and an additional voice channel can be obtained to enlarge system capabilities over conventional systems with no additional hardware costs and no additional bandwidth being occupied by the system.
Accordingly, it is an object of the present invention to provide a novel system and method to integrate a wireless telephone system into a private branch exchange or similar office telephone system
It is another object of the present invention to provide a novel system and method to utilize every available channel of a wireless system for voice (or data) messages.
It is yet another object of the present invention to provide a novel system and method for reducing power consumption within a portable unit without reducing capabilities of such a unit.
It is still another object of the present invention to provide a novel system and method which can be installed in an office environment without extensive wiring and/or substantial programming.
It is a further object of the present invention to provide a novel system and method of providing an integrated wireless-PBX telephone capability using housings which can be readily mounted on existing wall or ceiling surfaces of an office.
It is yet a further object of the present invention to provide a novel system and method of communicating in a wireless system in which base stations may readily be added to the system (or reset after a power outage) and brought on-line without extensive programming.
It is still a further object of the present invention to provide a novel system and method for accurately and efficiently communicating between plural wireless telephones and plural base stations